Interesting results Loading supers and subs with imr 4227

[Marksman1941]

Hi all! Newbie here. I’ve lurked and read a lot but haven’t signed up before today.

I have a PSA 10.5” 300blk with pistol length gas, psa bolt, and radian gas venting charging handle. The gun is suppressed with a SiCo Omega 30 can.

I finally got around to building some loads for it and am confused at my test results. I was testing in 40* weather, gusty winds, cloudy overcast day using a Caldwell chronograph set at 10’.

All loads used virgin starline brass and federal GMM 205 primers.

Super Loads were 110gr tactx seated to COAL 2.250”, ladder test in .3gr increments from 16.1gr IMR 4227 to 18.2gr IMR 4227. The Barnes webpage list 17.9gr as maximum for a velocity of 2162fps in a 16” test barrel. At my 18.2gr I had no brass deformation (even as soft as this starline brass is) and it was stupendously accurate. Velocities were averaging 1850fps. I know that an average of 50fps loss per barrel inch is common, but I was under the impression that the suppressor gave you back some of that velocity. I also figured a magnum pistol powder like 4227 wouldn’t be as affected by the shorter barrel. Are those velocity results in line with expectations? And I’ll do verification in the summer, but with zero pressure signs now do you think I’ll have problems when it hits 100* here?

Subsonic loads is where I got really confused. I loaded the reverse ladder of 11.0gr imr 4227 down to 10.2 gr under a 190gr subx. Same starline brass and federal GMM 205 primers. I don’t own a Hornady book, but have scoured this forum and the web enough to get a consensus that between 10-10.5gr it should be sitting right at 1000fps. Every load down to 10.4 gr was nearly 1100+ fps, and my 10.2gr load dipped into the 1050-1080 range. Much higher than I was expecting based on the temperature and the powder charge. Should I just keep working downward with 4227 until I hit a decent velocity? Or is that not the ideal powder for that game?

Finally, not a hand loading question (and one that has been beat to death and probably doesn’t need an answer). Shooting S&B 200gr subsonics at 900fps was still shockingly loud. My main comparison is a r700 in 308 that shoots 220gr Hornady rn on top of trail boss for truly movie quiet subsonics. The ar was a rackety loud monster compared to that. Every seems to suggest a JP silent capture spring and an adjust gas block. Is that still the two primary methods for reducing noise once you’re actually keeping things subsonic?

Thanks for the help in advance, and sorry for such a long winded first post!

[dpete]

You are right, an AR shooting subs is still a rackety monster to the shooter because of the BCG slamming back and forth next to your ear. To someone standing 10ft away its another matter, but still no where near as quiet as a bolt gun. Comparing bolt gun quiet and AR quiet is like comparing apples to oranges. You ain't ever gonna get one to be like the other. As I understand it, a silent capture spring reduces the spring twang inside the buffer tube, it probably won't do a thing for the clack of the BCG going back into battery. The BCG has to slam home no matter what spring is pushing it.

If you've got IMR 4227 you have the right powder for subs. Its all I use in 3 different sub loads and 3 different super loads using 125 and 150 gr bullets.

Just for reference 9.7 gr of 4227 is my go to for 220gr SMK. 970-980 fps is what my 8" barrel likes.

Real world data from my 4 Blackouts:
Bullets were 110gr Varmageddons and all were 5 shot groups. Powder is Lil'gun.

16" barreled Ruger American Ranch bolt action averaged 2502 fps

10.5" pistol AR averaged 2270 fps

8" SBR AR averaged 2176 fps

5" pistol AR averaged 1858 fps

[dpete]

On your sub loads I would expect you to use less 4227 than I do for your 190 gr bullets. My 220 SMKs use 9.7 gr to get to 980 fps. Your 10.2 gr load with a 190 at 1050+ makes sense. As long as you have a chronograph to check velocities you can keep going lower until you find a sub load that meets your accuracy needs. There is no harm in going under 1000fps as long as you like the accuracy. Just don't go so low that you stick a bullet in the barrel. Make sure that for every bang from the rifle a corresponding hole appears in the target

[BJK]

There is a also a telltale hisssss when a bullet gets stuck past the gas port, or there was with .223. You don't want to hear that sound. It might take e-muffs with the amplification turned all the way up to hear it. I don't remember and I'm not going to repeat it to find out.

[bangbangping]

On the supers, 1850 seems a bit slow but within reason. It's not uncommon to see speed variations of 200 fps from what you'd expect by looking at a manual. Different barrel, brass, powder, primer, yada yada yada. When I've checked, my suppressor added about 30 fps to a super load. Yours will be different, but probably not enough to matter. You could get more velocity with H110/W296.

Should I just keep working downward with 4227 until I hit a decent velocity?

Yep. Again, not uncommon. 4227 is a decent AR sub powder.

Pretty sure that everyone shooting their AR subsonic was disappointed the first time. I know I was. Now if I want quiet I shoot a bolt gun or a side-charging AR with the gas shut off. The things you mention can help some, but a cycling AR will never be quiet.

[Marksman1941]

Thank you all for the great replies. I figured the noise was just part of the ar platform at this point, and I'm really okay with it. I recognize that nothing will beat my bolt gun with 220gr RN in it, and to get relatively quiet with a reliably cycling semi auto is pretty awesome still.

I think my LGS has some H110 in stock, so I'll grab a couple pounds and see how the gun likes those. I did read that Starline brass seems to have a smaller internal capacity than most 300blk brass, which I would have expected to increase my velocities over what they were. But internal pressure physics still mystify me some days.

I'll keep working downwards with the IMR 4227. The only reason I was hesitant to go much further is most published data stops at the 10.5gr charge, and i've had weird issues with 4227 in my .44. For some silly reason i tried loading .44 special velocities in magnum cases with 4227, and got extremely erratic velocities (I'm assuming because of how little case fill there was). I realize that this is comparing apples to coconuts, but it did make me leery of going too low. Thanks for the reassurance that going lighter on the IMR is still safe in these subs

[dellet]

Sub loads rarely seem to follow the rules, and are often counter intuitive.

Example my 125 SST sub load is 11.5 grains 4227 in an 8” barrel.

If you want quiet, move to the fastest powder that will cycle you’re action. This is what commercial loads are so loud. They use very slow powders to insure cycling in poorly built actions.

You might lose 200 fps comparing your 16” bolt action to a 10.5” AR, but only 150 of that is due to barrel length. The other 50 is not having a gas port drilled into the barrel. You can shut off an adjustable block and watch the velocity increase.

If you slow down the cycling of your AR, noise will also decrease. Lots of tricks that can be utilized that really don’t require special parts. But none of that matters if you use a loud powder.

[dpete]

I recognize that nothing will beat my bolt gun with 220gr RN in it

Ummm maybe, maybe not. For a bolt gun load you can get stupid quiet using 110gr Varmageddons and Trail Boss powder to make subs. Somewhere in the neighborhood of 5 gr gets it done. We're talking Hollywood or BB gun quiet. Less bullet + less powder = less bang for the supressor to eat up. My Ruger American Ranch loves them.

[Marksman1941]

And that may be fair. I guess I was only speaking from what I've personally loaded, and 10.5gr of trailboss under a 220gr Hornady RN is ridiculously movie quiet but still hits surprisingly hard, even at 350 yards (once you figure out the ridiculous holdover you need for it). I've not experimented with smaller subsonics, but I'm sure if you're moving less air with less bullet and powder it makes sense that it would be quieter. I haven't found a need to step down much from the 220gr load (also works great with 9.8gr of TB under a 170 RN) so i haven't tried out the little 30cal bullets.

[Docstan72]

And that may be fair. I guess I was only speaking from what I've personally loaded, and 10.5gr of trailboss under a 220gr Hornady RN is ridiculously movie quiet but still hits surprisingly hard, even at 350 yards (once you figure out the ridiculous holdover you need for it). I've not experimented with smaller subsonics, but I'm sure if you're moving less air with less bullet and powder it makes sense that it would be quieter. I haven't found a need to step down much from the 220gr load (also works great with 9.8gr of TB under a 170 RN) so i haven't tried out the little 30cal bullets.

How are you fitting that much trail boss in a 300bo case? 6gn and my case runneth over.